Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density of the magnetic media. In this regard, so-called “perpendicular” recording media have been found to be superior to the more conventional “longitudinal” media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a “single-pole” magnetic transducer or “head” with such perpendicular magnetic media.
It is well-known that efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (i.e., as compared to the magnetic recording layer), magnetically “soft” underlayer or “keeper” layer, i.e., a magnetic layer having a relatively low coercivity of about 100 Oe or below, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the “hard” magnetic recording layer having relatively high coercivity of several kOe, typically about 3–6 kOe, e.g., of a cobalt-based alloy (e.g., a Co—Cr alloy such as CoCrPtB) having perpendicular anisotropy. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the hard, perpendicular magnetic recording layer. In addition, the magnetically soft underlayer reduces susceptibility of the medium to thermally-activated magnetization reversal by reducing the demagnetizing fields which lower the energy barrier that maintains the current state of magnetization.
A typical conventional perpendicular recording system 10 utilizing a vertically oriented magnetic recording medium 1 with a relatively thick soft magnetic underlayer, a relatively thin hard magnetic recording layer, and a single-pole head, is illustrated in FIG. 1, wherein reference numerals 2, 2A, 3, 3A, 4, and 5, respectively, indicate a non-magnetic substrate, an adhesion layer (optional), at least one magnetically soft underlayer, an amorphous or crystalline seed layer (optional), at least one non-magnetic interlayer, and at least one perpendicular magnetically hard recording layer. Reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of a single-pole magnetic transducer head 6. The at least one relatively thin interlayer 4 (also referred to as an “intermediate” layer), comprised of one or more non-magnetic materials, serves to (1) prevent magnetic interaction between the soft underlayer 3 and the hard recording layer 5 and (2) promote desired microstructural and magnetic properties of the hard recording layer.
As shown by the arrows in the figure indicating the path of the magnetic flux φ, flux φ emanates from single pole 7 of single-pole magnetic transducer head 6, enters and passes through vertically oriented, hard magnetic recording layer(s) 5 in the region above single pole 7, enters and travels along soft magnetic underlayer(s) 3 for a distance, and then exits therefrom and passes through the perpendicular hard magnetic recording layer 5 in the region above auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 1, vertical lines 9 indicate grain boundaries of each polycrystalline (i.e., granular) hard magnetic layer and interlayer of the layer stack constituting medium 1. As is apparent from the figure, the width of the grains of each of the polycrystalline hard magnetic layer(s) and interlayer(s) constituting the layer stack of the medium (as measured in a horizontal direction in the figure) may be substantially the same, i.e., each overlying layer may replicate the grain width of the underlying layer. A protective overcoat layer 11, such as of a diamond-like carbon (DLC), is formed over hard magnetic layer 5, and a lubricant topcoat layer 12, such as of a perfluoropolyether material, is formed over the protective overcoat layer.
Substrate 2 is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Al—Mg having an Ni—P plating layer on the deposition surface thereof, or substrate 2 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; adhesion layer 2A is typically comprised of an about 2 to about 5 nm thick layer of a material selected from the group consisting of Cr, CrTi, Ti, and TiNb; underlayer(s) 3 is (are) typically comprised of an about 500 to about 4,000 Å thick layer(s) of at least one soft magnetic material selected from the group consisting of NiFe (Permalloy), NiFeNb, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeAlN, FeSiAlN, FeCoC, FeCoB, FeCoTaZr, FeTaN, and FeTaC, or a laminated structure comprised of magnetic layers spaced-apart by thin spacer layers, such as of Ta, C, Si, etc., or a laminated structure comprised of magnetically soft layers spaced apart by anti-ferromagnetic coupling (AFC) layers, e.g., Ru, IrMn, etc.; amorphous or crystalline seed layer(s) 3A are typically comprised of an about 1 to about 5 nm thick layer(s) of at least one material selected from the group consisting of Pd, TiCr, Pt, Cu, Au, Ti, and Ag; interlayer(s) 4 typically comprise(s) an up to about 500 Å thick layer(s) of at least one non-magnetic material, such as Ru, Ti, CoCr, CoCrPt, CoCrTa, CoCrMo, etc.; and hard magnetic layer(s) 5 is (are) typically comprised of an about 50 to about 250 Å thick layer(s) of at least one Co-based magnetic alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, B, Ti, Zr, Hf, and Pd; and iron nitrides or oxides. The hard magnetic recording layer material has perpendicular anisotropy principally arising from magneto-crystalline anisotropy.
Notwithstanding the improvement (i.e., increase) in areal recording density and SMNR afforded by perpendicular magnetic recording media as described supra, the escalating requirements for increased areal recording density, media stability and SMNR necessitate further improvement in media performance.
As indicated above, perpendicular magnetic recording media typically include at least one magnetically soft underlayer for guiding magnetic flux through the media and to enhance writability, at least one non-magnetic intermediate or interlayer (hereinafter referred to as “interlayer”), and at least one main recording layer. The role of the interlayer(s) is critical for obtaining good media performance. Specifically, in perpendicular magnetic recording media the interlayer(s) serve to provide:
1. control of the crystallographic orientation of the main recording layer(s);
2. control of the grain size and grain distribution of the main recording layer(s);
3. destruction of exchange coupling between magnetically hard recording layers and magnetically soft layers; and
4. physical separation between adjacent grains of the main recording layer(s), which feature is particularly desirable and important when the latter is formed by a low temperature, high gas pressure sputtering process, and/or by a reactive sputtering process, so that an oxide, e.g., Co-oxide, occurs in the boundaries between adjacent grains.
More specifically, the SMNR of perpendicular magnetic recording media is improved by increasing the strength of the preferred c-axis out-of-plane orientation of the perpendicular main recording layer(s) while maintaining a small uniform grain size of the layer(s). The preferred orientation of the magnetic layer(s) depends upon the structural properties of and the interactions between the various previously deposited underlying layers of the media, as well as upon the nature of the substrate.
In general, control of the strength (or amount) of the preferred orientation of thin-film layers is difficult. Formation of a Co-alloy magnetic recording layer with a strong <0002> growth orientation on a structure including a substrate, a soft magnetic underlayer, and non-magnetic seed and interlayers between about 0.2 and 40 nm thick is extremely difficult.
Differences in crystallographic orientation between adjacent thin film layers are affected by the surface and interfacial energies of the materials of the layers, and by heteroepitaxial (or coherent) growth of one layer upon another layer of a chemically incompatible material with related crystal lattice structure and atomic interplanar spacings.
The soft magnetic underlayer of perpendicular magnetic recording media generally is composed of a small grain or amorphous material containing at least one of Fe and Co. According to prior practice, a non-magnetic material of hcp structure, e.g., Ru, may be deposited on the soft magnetic underlayer, which non-magnetic hcp material grows with a moderately strong <0002> preferred orientation and small grain size. A magnetic material of hcp structure, typically a Co-based alloy, may grow coherently on the hcp non-magnetic layer, also with <0002> growth orientation and small grain size. The quality of the <0002> growth orientation can be determined from the size of symmetric X-ray diffraction (“XRD”) peaks and rocking curves. Strong preferred growth orientation of the Co-based alloy with the hcp <0002> axis out-of-plane is generally necessary for achieving good performance of high areal recording density perpendicular magnetic media. Unfortunately, however, the quality of growth orientation of an hcp material upon the soft magnetic underlayer depends upon the selected material, and prior intermediate or underlayer structures, such as with a Ru layer and a Co-alloy layer, generally have not afforded the desired strength of <0002> growth orientation.
As indicated supra, one type of perpendicular magnetic recording media comprises Co alloy-based recording layers wherein oxides are present between adjacent magnetic grains for enhancing inter-granular separation. Such layers are typically formed by a sputtering process performed at a high pressure, e.g., about 30 mTorr, with Ru alloy-based films utilized as interlayers beneath the recording layer(s). When the Ru alloy-based interlayers are deposited, as by sputtering at a relatively high gas pressure, the physical separation between neighboring grains afforded by the oxides and/or voids promotes de-coupling of the magnetic grains and enhances the coercivity of the layer. However, the crystallographic (0002) orientations of the Ru/Co-alloy interlayer/magnetic alloy bi-layer structure are not as good as when the Ru interlayer is sputter-deposited at a lower pressure.
The above-described behavior may be demonstrated by reference to FIG. 2, which presents, in graphical form, the variation of the full-width at half-maximum (FWHM) of XRD (X-ray diffraction) rocking curves and coercivity (Hc) of perpendicular magnetic media of the following structure: 200 nm FeCoB soft magnetic underlayer/30 nm Ru interlayer/9 mm CoCrPtOx perpendicular recording layer/4.2 nm C protective overcoat layer, as a function of the gas pressure during sputter deposition of the Ru interlayer.
As is evident from FIG. 2, media for which the Ru interlayer is deposited at a lower gas pressure (i.e., ˜0.8 mTorr) during sputter deposition have narrower FWHM of the Ru/Co (0002) peaks of the XRD rocking curves than media for which the Ru interlayer is deposited at a higher sputter gas pressure (˜7 to ˜30 mTorr). However, the coercivity (Hc) of the media is significantly higher when the Ru interlayer is deposited at the higher sputter gas pressures, which high coercivities are much desired. From a consideration of these apparent competing factors or tendencies, it is apparent that the problem/drawback of poor crystallographic orientations of media (i.e., with wide FWHM) wherein the Ru interlayer is deposited at the higher sputter gas pressures requires resolution.
In view of the above-demonstrated critical nature of the intermediate or interlayer in obtaining high performance perpendicular magnetic recording media, there exists a clear need for improved film or layer structures for facilitating highly oriented crystal growth thereon, and for highly crystallographically oriented perpendicular magnetic recording media comprising improved intermediate or interlayer structures for providing enhanced performance characteristics.
The present invention, therefore, addresses and solves problems attendant upon the design and manufacture of improved film or layer structures for facilitating highly oriented crystal growth and fabrication of high performance, ultra-high areal recording density perpendicular magnetic recording media, while maintaining full compatibility with the economic requirements of cost-effective, large-scale, automated manufacturing technology.